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/*:
 
 #70 [Climbing Stairs](https://leetcode.com/problems/climbing-stairs/description/)
 
 You are climbing a stair case. It takes n steps to reach to the top.
 
 Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?
 
 Note: Given n will be a positive integer.
 
 Example 1:
 ```
 Input: 2
 Output: 2
 Explanation: There are two ways to climb to the top.
 1. 1 step + 1 step
 2. 2 steps
 ```
 
 Example 2:
 ```
 Input: 3
 Output: 3
 Explanation: There are three ways to climb to the top.
 1. 1 step + 1 step + 1 step
 2. 1 step + 2 steps
 3. 2 steps + 1 step
 ```
 
 */
import Foundation

class Solution {
    func climbStairs(_ n: Int) -> Int {
        if n < 4 {
            return n
        }
        
        var prevPrev = 2
        var prev = 3
        var count = 4
        while count != n {
            var newPrev = prevPrev + prev
            prevPrev = prev
            prev = newPrev
            count += 1
        }
        return prevPrev + prev
    }
}

print(Solution().climbStairs(2))
print(Solution().climbStairs(5))

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